The present invention relates to a sizing composition comprising an aqueous dispersion of a rosin material and a polyaluminium compound, and to a method of sizing a cellulosic fibre material.
One of the main properties of paper, paperboard and similar products is hydrophobation or resistance to penetration by water and other liquids, such as lactic acid, hydrogen peroxides solutions, etc. Hydrophobation also plays an important role in printing properties, affecting the way inks are adsorbed on paper products. The two main methods for conferring hydrophobic properties to paper products are internal sizing, which gives a hydrophobic effect in the entire paper structure, surface sizing, more or less limited to the actual surface structure, and a combination of both methods. The most common hydrophobic agents in internal sizing are rosin, synthetic sizing agents, such as alkyl ketene dimers, isocyanates, acid anhydrides and carbamoyl chlorides and combinations of both components.
It has recently been experienced, however, that the initial liquid packaging board resistance to edge penetration by lactic acid and hot hydrogen peroxide-containing solutions achieved by traditional products or methods is not always maintained over time, which often means economic, converting and end-use problems. In addition, deficient ink jet properties, such as wicking, drying time, color appearance, etc, also imply serious end-use problems.
It has been shown that internal sizing with a cationic rosin size (CRS), such as those disclosed in ES-8900750, GB-2159153, EP-O-200002, U.S. Pat. No. 3,966,654 and U.S. Pat. No. 4,199,369, or with a conventional anionic rosin size (emulsion, paste or soap) gives the finished paper good resistance to penetration by water, but it also has some drawbacks, such as some limitations in pH and temperature, the difficulty to give the paper a good resistance to penetration by acid liquids or the need to be used in comparatively high amounts to give a satisfactory sizing effect. On the other hand, rosin dispersions are widely used and cannot in all circumstances be replaced by synthetic sizing agents; rosin dispersions give, for example, a good adhesion to yankee cylinders.
Synthetic sizing agents react with the cellulose to give an irreversible bond. Although these sizing agents generally lead to a very good sizing effect, both to water and other liquids, they do also have some disadvantages. For example, sizing must be carried out at neutral or slightly alkaline pH""s (between 7 and 8.5) to be effective, there is a risk of hydrolysis in water and synthetic sizing agents cannot give the finished paper a good resistance to penetration by hot peroxides. Moreover, although synthetic sizing agents give good ink holdout and brighter colors, some other ink jet properties are relatively poor, such as wicking, drying time or color-to-color bleed.
It is known to combine rosin and some synthetic sizing agents, which allows to overcome some of the aforementioned disadvantages when they both are used alone. For example, EP-A-0074544 discloses a method of sizing using cationic dispersions which contain as dispersed phase particles of fortified rosin as well as particles of the synthetic sizing agent. EP-O-275851 discloses a method of sizing utilizing the above cationic and anionic dispersions which further contain a polyaluminium compound. DE-A1-41 03 169 discloses a sizing composition including a conventional sizing agent together with an aluminium phosphate that contains on the average 1.5-3 phosphor atoms per aluminium atom. EP-O-693589 discloses a method of sizing paper and similar cellulose products containing precipitated calcium carbonate as a filler using the above dispersions. In WO 96/35841 a watersoluble inorganic alkali metal salt is added to improve the stability of cationic dispersions of sizing agents based on rosin and cellulose reactive material. U.S. Pat. No. 4,522,686 discloses a sizing composition in the form of an aqueous dispersion containing a cellulose-reactive sizing agent, fortfied rosin and a water-soluble, nitrogen containing dispersing agent, the last two components forming the elements of a CRS. EP-A-0 292 975 discloses a method for use in producing liquid packaging board. However, in the above publications there is no suggestion that there is a particular problem caused by the decrease in the resistance to edge-penetration by hot hydrogen peroxide-containing solutions, namely the board is within specifications at the reel, but, upon ageing, this resistance decreases to a level where it then remains constant. There is no suggestion, either, that there is a particular problem caused by deficient ink jet properties, such as wicking, drying time or color-to-color bleed.
Moreover, dispersions of sizing agents can exhibit stability problems whose practical consequences are a markedly increased viscosity, agglomeration and phase separation, which may lead to depositions, difficulty in dosing and deteriorated sizing.
It is an object of the present invention to provide a sizing composition and a method of sizing a cellulosic fibre material that reduce or eliminate the above disclosed problems associated with the prior art, and more particularly to provide a sizing composition with enhanced stability and which gives improved long time resistance to edge penetration by lactic acid and hot hydrogen peroxide-containing solutions when the composition is used for sizing cellulosic fibre materials such as paper, board and paper board.
According to the invention it has been found that the above problems may be alleviated or eliminated and superior results achieved by using as a polyaluminium compound in the sizing composition a polyaluminium phosphate sulphate (PAPS) compound. It has been found that polyaluminiumphosphate sulphates present in the sizing dispersion strongly enhances its sizing effect as compared to non-phosphate containing polyaluminium salts.
Thus, according to one aspect the present invention provides a sizing composition comprising an aqueous dispersion of a rosin material and a polyaluminium compound, characterised in that the polyaluminium compound is a polyaluminium phosphate sulphate compound.
According to another aspect the present invention provides a method of sizing a cellosic fibre material, such as paper, board or paper board, characterised in that the above sizing composition is added to the cellulosic fibre material in an amount of 0.01-5% by weight, calculated as dry sizing agent on dry cellosic fibres.
The dispersions according to the invention have low tendency to agglomerate and separate on storage, showing very good shelf life.
It has also been found that such dispersions used in the process for making a board for a container for consumable liquids gives its cut edges a high resistance to penetration by hot hydrogen peroxide and lactic acid and avoids the loss of such resistance upon ageing. Moreover, sizing with the dispersions described in the present invention give very good ink-jet properties such as wicking, drying time, color-to-color bleed or color appearance, overcoming the problems caused by a poor response. These surprising effects are even more unexpected since it was found that the use of a synthetic sizing agent, such as AKD, rosin size and alum or, alternatively, the use of combinations of rosin and synthetic sizing agents, such as those described in the aforementioned patents, did not give the same sizing effects. The polyaluminium compounds of the present invention differ substantially from the prior art polyaluminium compounds, especially the polyaluminium sulphates described for example in WO 94/01619 and EP-62015.
These and other advantages and characterising features of the present invention will appear from the following specification and the appended claims.
The superior results achieved with the polyaluminium compound of the present invention are beleived to be due to the incorporation of phosphate into the polyaluminium compound. In addition to the phospate ions the compound also includes sulphate ions and hydroxide ions as counter ions. Sometimes chloride ions may occur in minor amounts as a contamination.
Preferably, the polyaluminium phosphate sulphate compound of the present invention has the following general formula (I):
[Al(H3PO4)x(OH)y(SO4)(3xe2x88x92y)/2]nxe2x80x83xe2x80x83(I)
where 0,01xe2x89xa6xxe2x89xa60,5 and 0,03xe2x89xa6yxe2x89xa62,5 and n is an integer xe2x89xa71.
Preferably, x lies in the range of 0,02-0,3 and y lies in the range of 0,2-2,2.
The charge of the ortho-phosphate depends on the pH. The pH of polyaluminium salt solutions depends on the basicity, aluminium concentration and temperature of the solution. At room temperature most polyaluminium salts have a pH in the range of 0-4. The pKal of phosphoric acid is 2,15. In strongly basic or in diluted polyaluminium phosphate salt solutions some of the phosphate may be present as H2PO4xe2x88x92. For the sake of simplicity the presence of phosphate in the above formula (I) is shown as phosphoric acid. The factors x and y in the formula hold irrespectively in which form the phosphate is present.
Depending on the method used when producing the polyaluminium phosphate sulphate it may also contain a neutral salt such as Na+, K+, NH4+, Ca2+or Mg2+ sulphate, chloride or formate.
The polyaluminium phosphate sulphate(PAPS)compound according to the invention can be prepared by dissolving aluminium sulphate, adding aluminium metal to the solution, refluxing the mixture and adding phosphoric acid to the mixture.
In the aqueous dispersion the polyaluminium phosphate sulphate compound is preferably present in an amount of at least 5% by weight, more preferably 20-60% by weight, calculated as aluminium on the amount of rosin material of the sizing composition.
The sizing agent in the dispersions according to the invention may comprise only rosin material or rosin material in combination with synthetic sizing agents.
The rosin material used in the dispersions according to the invention should have a high free rosin content. Rosin and rosin material herein otherwise refer to known types of rosin such as gum-, wood-, tall oil rosin and mixtures thereof. The rosin-based sizing agent can be selected from rosin, modified rosin, fortified rosin and mixtures thereof. Modified rosin is rosin that has been modified in a known manner, such as for example disproportionated rosin, hydrogenated rosin, polymerized rosin, esterified rosin, etc. The rosin material is preferably fortified rosin, i.e. a Diels Alder adduct obtained in a known manner by the reaction between rosin, optionally modified as above, and an xcex1, xcex2-unsaturated carbonyl compound, i.e. fumaric acid, maleic acid or their anhydrides or half esters, acrylic acid and methacrylic acid. In combinations according to the present invention the degree of fortification of the rosin material can reach up to about 15 per cent by weight of adducted xcex1, xcex2-unsaturated carbonyl compound, based on the total weight of the fortified rosin.
The amount of rosin component present in the rosin-based sizing agent is preferably in the range of from about 25 to about 95% by weight based on the total amount of rosin-based sizing agent. Preferably the rosin component is present in an amount from about 15% to 50% by weight.
In addition to the rosin material the sizing composition of the present invention preferably also comprises a synthetic sizing agent. Synthetic sizing agents are well known in the art and preferably includes at least one member selected from the group consisting of ketene dimers, acid anhydrides, organic isocyanates, and carbamoyl chlorides.
When the sizing composition comprises both a rosin material and a synthetic sizing agent the rosin material comprises up to 95% by weight, preferably 10-95% by weight, based on the total weight of the rosin material and the synthetic sizing agent.
The synthetic sizing agents in the mixed particles in the present dispersions are preferably selected from the group consisting of ketene dimers, acid anhydrides, organic isocyanates, carbamoyl chlorides and miztures thereof. Ketene dimers (AKD) are preferred. They have the general formula: 
wherein both R1 and R2 represent hydrocarbon groups having about 6 to about 30 carbon atoms, usually being alkyl groups having 12 to 20 carbon atoms, such as hexadecyl and octadecyl groups.
The aqueous dispersion of the sizing composition of the invention preferably has a dry content of at least 1% by weight, more preferably at least 5% by weight. The upper limit of the dry content depends on the type of sizing agent used and usually is about 50% by weight.
In the dispersions of the present invention the dispersed phase consists of particles of a mixture of rosin and synthetic sizing agent whereby the mixture contains from 10 to 95% by weight of rosin. As the particles contain a homogeneous mixture of the active sizing agents the weight ratio in each particle in the dispersion will thus be in this range.
Dispersions of mixed particles may be prepared without using any dispersing agent. Alternatively and preferably, dispersions may be prepared using one or several dispersing agents selected from anionic, cationic or non-ionic dispersing agents. The amount of dispersing agent should be sufficient to give the dispersions the desired storage stability. The upper limit is not critical, but normally it is sufficient to use no more than 5% by weight, preferably 0.1-5% by weight.
Cationic dispersing agents can for example be selected from nitrogen containing dispersing agents such as quaternary ammonium compounds and salts of tertiary amines. Protective colloids or retention agents, such as catinonic starch, casein, cellulose derivatives, guar gum, polyvinylalchol, polyacrylamide, polyethyleneimine, polyamine, polyamidoamine, polyethyleneamine or polyacrylate can also be included in the dispersions. Anionic surfactants can be selected from alkyl sulphates, alkyl sulphonates, alkylarene sulphonates, i.e. sodium lauryl sulphate or sodium lignosuphonate. Nonionic dispersing agents can for example be alkoxylated alcohols, alkylphenols and fatty acids, partial fatty acid esters of polyvalent alcohols with 2 to 8 carbon atoms, or anhydro derivatives of these, and alkolylated derivatives of these.
The dispersion according to the invention can contain dispersed particles of rosin-based sizing agent and ispersed particles of synthetic sizing agents, or dispersed particles containing a mixture of rosin based sizing agent and synthetic sizing agents, or a combination of the mentioned dispersed particles. Dispersions containing discrete particles of rosin-based sizing agent and synthetic sizing agents can be prepared by mixing a preformed dispersion of rosin-based sizing agent with a preformed dispersion of synthetic sizing agents.
Aqueous cationic dispersions of rosin-based sizing agents are commercially available or can be prepared in a per se conventional manner, e.g. by homogenizing the active substance in water in the presence of a dispersing agent using high shear forces and high temperatures so that fine particles are obtained as the dispersed phase. The active substance which is homogenized is a rosin component. The active substance is dispersed in water in the presence of a dispersing agent under satisfactory agitation. The warm dispersed phase is then cooled and mixed with the polyaluminium phosphate sulphate compound. The final dispersion is homogenized.
Aqueous dispersions or emulsions of synthetic sizing agents are known in the art and commercially available and such dispersions can be prepared in a per se conventional manner, e.g. by mixing the synthetic sizing agent with an aqueous solution of a dispersing agent or emulsifier and passing the mixture through a homogenizer.
The novel dispersions of this invention can be prepared by mixing of a rosin-based dispersion, and a synthetic sizing agent dispersion. Modification of the above procedures are also suitable and within the skill of the art to which the invention pertains.
The present dispersions are particularly suitable for sizing of paper, board, paper board and similar cellulose fibre products. The dispersions can be used for internal and surface sizing. The dispersions are preferably used for internal sizing and are added in a conventional manner to a cellulose stock and conventionally used chemicals at paper production, such as drainage and/or retention agents, aluminium compounds, fillers, wet strength resins, dyes, optical brightening agents, etc, can of course be used with the present dispersions. The dispersions can be used in an amount corresponding to 0.01 to 5% by weight of sizing agent, counted as dry on dry cellulose fibres, suitably in an amount corresponding to 0.025 to 1% by weight of sizing agent.
The invention is further illustrated in the following examples, which, however, are not intended to limit the same. Parts and percentages relate to parts by weight and per cent by weight, respectively, unless otherwise stated.